Digestive tract radiography is essential to medical examinations for the treatment and prevention of various digestive diseases. Particularly, cancer of the digestive tract is detected at high ratios by radiography; therefore, not only patients with suspected cancer but also healthy persons, for the purpose of secondary prophylaxis, often undergo cancer examination by radiography.
The representative radiographic contrast media for digestive tract radiography are barium preparations containing barium sulfate as the active ingredient. Barium preparations possess an excellent contrast effect and chemical stability and, in addition, they are cheap. However, they are often accompanied by a problem of side effects on digestive organs such as constipation. Also, barium preparations are not applicable to those patients with perforation or acute bleeding in the digestive tract or those suspected of such a lesion. These side effects and use limitations are associated with the astringent action of barium sulfate and its nature in which it becomes clayish and solidifies like gypsum in the absence of sufficient water due to its poor fluidity and adhering and condensing properties. In fact, purgatives and other medicines are used in combination with these preparations to cope with the side effects, but this measure is not satisfactory. To solve the above-mentioned problem posed by the barium preparations, an aqueous iodic preparation has been proposed. This preparation, containing meglumine sodium amidotrizoate as the active ingredient, has no digestive tract side effects as found in barium preparations and is thus applicable to patients in whom the use of barium preparations is contraindicated. However, this preparation involves a risk of iodine shock as the most critical side effect. Iodine shock is not a frequently-occurring side effect, but it may cause serious symptoms, which may lead to death. For this reason, the use of this preparation is contraindicated for patients with a past history of iodine hypersensitivity, and much care should be given when applying it to patients with allergic constitution. In addition, the aqueous iodic preparation is relatively expensive.
Accordingly, none of the currently used radiographic contrast media are perfect. With this background, it was desired that a radiographic contrast medium which has an excellent radiographic contrast effect without severe side effects should be developed.